CN-115029393-B - Method for producing medium chain fatty acid from straw based on DES additive

CN115029393BCN 115029393 BCN115029393 BCN 115029393BCN-115029393-B

Abstract

The invention provides a method for producing medium-chain fatty acid from straw based on a DES additive, and belongs to the technical field of medium-chain fatty acid extraction. According to the method for producing medium-chain fatty acid from straw based on the DES additive, disclosed by the invention, the planting waste straw is treated by adopting the DES with the hydrogen bond acceptor being choline chloride, so that the utilization rate of agricultural waste is improved, and the process of producing medium-chain fatty acid from anaerobic fermentation is promoted. The pretreatment before anaerobic fermentation and the thermal shock effect in the anaerobic fermentation process have better straw depolymerizing effect, inhibit the methane-producing flora in the medium-temperature anaerobic fermentation, inhibit the generation of methane in the continuous anaerobic fermentation process and ensure the maximum utilization of straw for producing medium-chain fatty acid. The method solves the problems that the process of producing medium-chain fatty acid by straw anaerobic fermentation has methane production tendency, the substrate is difficult to be completely utilized, the electron donor is insufficient in the process of producing acid, the fermentation efficiency is low, and the like.

Inventors

LUO JUAN
ZHAO LIXIN
HOU XINTONG
YAO ZONGLU
YU JIADONG

Assignees

中国农业科学院农业环境与可持续发展研究所
中国农业科学院农业环境与可持续发展研究所

Dates

Publication Date: 20260421
Application Date: 20220726
Priority Date: 20220726

Claims (6)

1. A method for producing medium chain fatty acid by straw based on DES additive, which is characterized by comprising the following steps: (1) Anaerobic fermentation liquid preparation, namely placing a mixture of a DES additive, straw, anaerobic granular sludge and water into a continuous stirring reactor, uniformly mixing, and adjusting the pH value of the mixture to 5-5.5 by adopting 0.1mol/L dilute hydrochloric acid; (2) Pretreatment before fermentation, namely, before the anaerobic fermentation process begins, carrying out thermal shock pretreatment on the mixture in a stirring reactor to realize DES depolymerization of straw and inhibit methanogen growth and reproduction; (3) Anaerobic fermentation of the mixture after the pretreatment in the step (2), collecting the generated gas by a gas collecting bag, detecting the methane content in the gas every day, carrying out the variable-temperature thermal shock treatment when the methane content is higher than 20%, and then continuously carrying out anaerobic fermentation to produce medium-chain fatty acid, wherein when the methane content is lower than 20%, the medium-chain fatty acid is continuously produced by anaerobic fermentation at 37 ℃; The hydrogen bond acceptor of the DES additive is choline chloride, the hydrogen bond donor is one or two of lactic acid and acetic acid, and the adding amount of the DES additive is calculated according to the concentration of the hydrogen bond donor of 5-10 g/L; The preparation method of the DES reagent in the step (1) comprises the steps of mixing a hydrogen bond acceptor and a hydrogen bond donor according to a molar ratio of 1:1-5, and stirring for 2 hours in a 70 ℃ oil bath; The thermal shock pretreatment method in the step (2) comprises the steps that when the lignin content in the straw is less than or equal to 10%, the pretreatment temperature is 60-80 ℃, the pretreatment time is 3-5 hours, and when the lignin content in the straw is greater than 10%, the pretreatment temperature is 80-100 ℃ and the pretreatment time is 5-10 hours; The specific method of the variable-temperature thermal shock treatment in the step (3) comprises the steps of raising the fermentation temperature to 80 ℃ for thermal shock for 1h, naturally cooling to 37 ℃ after thermal shock, and continuing anaerobic fermentation; The anaerobic fermentation is carried out at the temperature of 37+/-1 ℃, the hydraulic retention time is 20-32 d, the quantitative feeding is 3-5% per day, the quantitative discharging is 3-5%, and the continuous stirring speed is 10-20 rpm/min; and (3) continuously adding a DES reagent into a continuous stirrer in the anaerobic fermentation process, continuously providing electron donor lactic acid and short-chain acid acetic acid for the reaction process, and promoting the process of producing medium-chain fatty acid by anaerobic fermentation.
2. The method for producing medium-chain fatty acid by using straw based on a DES additive according to claim 1, wherein the hydrogen bond acceptor of the DES additive in the step (1) is choline chloride, the hydrogen bond donor is one or both of lactic acid and acetic acid, and the addition amount of the DES additive is calculated according to the concentration of the hydrogen bond donor of 5-10 g/L.
3. The method for producing medium-chain fatty acid from straw based on DES additive as claimed in claim 1, wherein the preparation method of DES reagent in step (1) comprises mixing hydrogen bond acceptor and hydrogen bond donor according to a molar ratio of 1:1-5, and stirring in 70 ℃ oil bath kettle for 2h.
4. The method for producing medium-chain fatty acid by using straw based on DES additive as claimed in claim 1, wherein the mass ratio of straw to anaerobic granular sludge dry matter in the step (1) is 1:2-5, the total solid content TS of anaerobic granular sludge is 5% -15%, the granularity is 60% -70%, and the particle diameter is 0.5-4 mm.
5. The method for producing medium-chain fatty acid from straw based on DES additive as claimed in claim 1, wherein the stirring reactor in the step (2) adopts a continuous stirring mode, and the stirring speed is 100-120 rpm/min.
6. The method for producing medium chain fatty acid from straw based on DES additive according to claim 1, wherein the DES reagent is added in an amount of 1.5-2 g/L every 2 days.

Description

Method for producing medium chain fatty acid from straw based on DES additive Technical Field The invention relates to the technical field of medium-chain fatty acid extraction, in particular to a method for producing medium-chain fatty acid from straw based on a DES additive. Background The agricultural waste contains a large amount of lignin, and related researches in the fields of producing methane by anaerobic fermentation of plant waste straws, producing medium-chain fatty acid by anaerobic fermentation, producing sugar by enzymolysis and the like are quite numerous at home and abroad, and anaerobic digestion is a technology capable of converting the plant waste into renewable energy. The yield of the medium-chain fatty acid can be promoted by adding an electron donor or a short-chain acid in the process of producing the medium-chain fatty acid by anaerobic fermentation, wherein the common electron donor is lactic acid, the common short-chain acid is acetic acid, and the process of promoting the production of the medium-chain fatty acid by the pretreated straw is less researched at home and abroad at present. Chinese patent CN111394401a discloses a method for preparing medium-chain fatty acid by anaerobic fermentation of lignocellulosic raw material, firstly, lignocellulose is converted into short-chain fatty acid by anaerobic acidification under alkaline condition, then the short-chain fatty acid is converted into medium-chain fatty acid with higher added value by secondary anaerobic fermentation, and finally the medium-chain fatty acid with higher concentration is obtained by separation and extraction technology. Chinese patent CN110734934a discloses a method for promoting anaerobic fermentation of excess sludge to produce medium-chain fatty acid by pretreatment, which utilizes free nitrous acid to promote dissolution of organic substances in sludge, and improves the hydrolysis rate of sludge, thereby improving the yield of medium-chain fatty acid in anaerobic fermentation system. Chinese patent CN110656133a discloses a pretreatment method for promoting anaerobic fermentation production of medium-chain fatty acid by using waste activated sludge from secondary sedimentation tank of municipal sewage treatment plant as fermentation substrate, adding ammonium chloride solution, controlling pH and temperature to pretreat Free Ammonia (FA), adding pretreated sludge into anaerobic reactor, adding electron donor, and anaerobic fermentation production of medium-chain fatty acid. However, the methane inhibitor is added during the treatment process of the method. The Deep Eutectic Solvent (DES) is a eutectic mixture composed of Hydrogen Bond Donors (HBD) and Hydrogen Bond Acceptors (HBA), researches show that the DES with the HBA being choline chloride (ChCl) has an effect of promoting the anaerobic fermentation process, and the DES is a good reagent for preprocessing straw, and can promote the depolymerization of the straw, so that the utilization rate of the straw is improved. Disclosure of Invention In view of the above, the invention aims to provide a method for producing medium-chain fatty acid from straw based on a DES additive, which adopts DES with a hydrogen bond acceptor of ChCl (choline chloride) to treat planting waste straw, improves the utilization rate of agricultural waste and promotes the process of producing medium-chain fatty acid from anaerobic fermentation. Solves the problems that the process of producing medium-chain fatty acid by straw anaerobic fermentation has methane production tendency, substrates are difficult to be fully utilized, electron donors are insufficient in the process of producing acid, the fermentation efficiency is low, and the like. The invention relates to a method for producing medium chain fatty acid by straw based on a DES additive, which comprises the following steps: (1) Anaerobic fermentation liquid preparation, namely placing a mixture of DES additive, straw, anaerobic granular sludge and water into a continuous stirring reactor, uniformly mixing, and adjusting the pH of the mixture to 5-5.5 by adopting 0.1mol/L dilute hydrochloric acid, wherein the straw is one or more of silage corn straw, dry corn straw, wheat straw, rice straw, sorghum straw, cotton straw and sugarcane leaves or bagasse; (2) Pretreatment before fermentation, namely, before the anaerobic fermentation process begins, carrying out thermal shock pretreatment on the mixture in a stirring reactor to realize DES depolymerization of straw and inhibit methanogen growth and reproduction; (3) And (3) carrying out variable-temperature thermal shock treatment in the fermentation process, namely carrying out anaerobic fermentation on the mixture pretreated in the step (2), collecting generated gas by a gas collecting bag, detecting the methane content in the gas every day, carrying out variable-temperature thermal shock treatment when the methane content is higher than 20%, and continuously carrying out